There have been known, as light emitting elements, light emitting diodes (hereinafter, simply referred to as “LEDs”) each containing a semiconductor multilayer film. Especially, GaN LEDs emitting blue light are applicable to a light emitting device or the like emitting white light in combination with a wavelength conversion member containing a phosphor material (hereinafter, also referred to as “phosphor”) for converting a wavelength of blue light into a wavelength of yellow light (see Patent Literature 1, for example).
Here, the above phosphor is a phosphor containing a light absorbing material that absorbs wavelengths of at least part of light emitted from LEDs, a phosphor containing a fluorescent material that is excited by light emitted from LEDs and thereby emits light having a wavelength different from a wavelength of light emitted from the LEDs, and the like.
As the above wavelength conversion member for use in a light emitting device utilizing LEDs, the following have been conventionally employed: a wavelength conversion member that is made of a phosphor paste, which is obtained by dispersing a phosphor in a translucent resin such as a silicone resin, is provided on an upper surface of an LED, and a phosphor having a high density that is precipitated and is arranged immediately adjacent to the LED; a wavelength conversion member made of a phosphor paste formed beforehand to be plate-like that is arranged on or applied to the upper surface of the LED; a wavelength conversion member made of a phosphor paste that is arranged directly on the upper surface of the LED by a print method, a potting method, or the like; a wavelength conversion member made of a so-called ceramic plate formed beforehand in which a phosphor is included that is applied on the upper surface of the LED.
In the case where a wavelength conversion member containing a phosphor is applied in combination with LEDs as described above, the optical properties can be controlled by adjusting the thickness of the wavelength conversion member (see Patent Literatures 2 and 3, for example).
Also, the optical properties can be similarly controlled by adjusting the concentration of a phosphor material contained in the wavelength conversion member.
That is, in order to exhibit required optical properties of light obtained by combining light emitted from LEDs and light wavelength-converted by the wavelength conversion member, the light emitting device such as described above is designed to have the thickness of the wavelength conversion member, the concentration of the phosphor material, and so on based on the intensity and wavelength of light.